def unregister_referenced_index(sender, **kwargs):
"""Unregister a :class:`ObjectIndex` if there isn't any references to it."""
instance = kwargs['instance']
#get the key referencing the ObjectIndex class
fkeys = foreign_keys(instance.__class__)
fkeys.update(many_to_many_fields(instance.__class__))
index_key = None
for key, details in fkeys.items() :
if issubclass(details['class'], ObjectIndex) :
index_key = key
break
#if found get the ObjectIndex instance
#its reverse foreign keys and reverse many to many fields
#then detect if some relationships remain
#and finally delete the ObjectIndex instance
#if it is not the case
if index_key :
index = getattr(instance, index_key)
keys = reverse_foreign_keys(ObjectIndex).keys()
keys.extend(reverse_many_to_many_fields(ObjectIndex).keys())
for key in keys :
count = getattr(index, key).all()
if count :
return
index.delete()
def get_links(cls):
"""
Get fields materialising dependencies between 2
classes that don't lead to a delete cascading.
"""
dct = SortedDict()
dct.update(many_to_many_fields(cls))
dct.update(reverse_many_to_many_fields(cls))
return dct
